Well casing and method for threading

ABSTRACT

A swaging machine has a head with an axis of rotation and a plurality of holes spaced in a circular array concentric and parallel with the axis of rotation. Shafts extend from each of the holes, each shaft having a supporting portion located on the forward side of the head. Rollers are rotatably mounted to the supporting portions of the shaft, each roller having a conical exterior. A chucking member on the rearward side of the head is engaged by a rotary member to rotate the head. The rollers of the rotating head are brought into engagement with a cylindrical pipe, causing a tapered swaged section to be formed on the end of the pipe. The pipe is then threaded. The pipe is preferably of small wall thickness.

FIELD OF THE INVENTION

[0001] This invention relates in general to well casing, particularly a method for threading thin wall well casing that includes a preliminary step of swaging.

DESCRIPTION OF THE PRIOR ART

[0002] Well casing of the type concerned herein is made up of sections of pipe each typically about 38 to 43 feet in length. Each section of pipe has external threads on both ends. The pipe sections are joined by collars that have internal threads.

[0003] The threads are normally a standard API thread that is formed with a taper. That is, the crests of the threads will taper from a larger diameter to a reduced diameter at the end of the pipe. The threads are form-ed in a conventional manner using equipment that cuts them on the cylindrical end of the pipe.

[0004] This method works well enough if the pipe wall thickness relative to the taper angle and the depth of the threads is sufficient. The threads at the end will still have adequate supporting metal and the depth of each thread remains constant throughout the threaded section.

[0005] However, there are occasions where thinner wall pipe is desired, such as in shallow gas wells. With very thin wall pipe, the supporting metal under the threads decreases near the end of the pipe because of the conical taper of the thread crests. At the extreme end of the pipe, the threaded section may not have adequate gripping strength because of the thinness of the supporting metal. As a result, when attached to a threaded collar and pulled in a tensile test, the threaded sections may pull apart from each other.

[0006] A procedure has been used in the past on some tubular members that increases the wall thickness of the pipe near the pipe rim so that the threads will have adequate supporting metal throughout the threaded section. In that procedure, first, the outer diameter of the tubular member is swaged to provide a conical taper. Then, the threads are cut on the conical taper. To applicant's knowledge, this has been performed only with heavier wall pipe for use in high pressure installations, such as proprietary type connections that form metal to metal seals. The wall thickness of such pipe before swaging is typically in excess of 0.275″. Also, the swaging operation is a slow process because of the equipment utilized.

SUMMARY OF THE INVENTION

[0007] The swaging apparatus of this invention has a head with an axis of rotation and a plurality of holes spaced in a circular array, concentric and parallel with the axis of rotation. Shafts are located in each of the holes, each of the shafts having a supporting portion on a forward side of the head. A roller is rotatably mounted to a supporting portion of each of the shafts. Each of the rollers has a tapered exterior. A chucking member is located on the rearward side of the head for engagement by a rotary member to rotate the head.

[0008] This apparatus is used to swage thin walled pipe for use as well casing. The pipe is held stationary while the swaging head is rotated. The head and pipe are brought together, with the rollers forming a conical taper on an end section of the pipe. The swaged taper is preferably equal to or less than the thread taper. Conventional threads are formed on the tapered exterior.

[0009] Preferably the pipe has an outer diameter in the range from 4½″ to 5½″ and a wall thickness from about 0.125″ to 0.219″. The swaged taper is preferably in the range from about 0.035 to 0.0625 inch per inch, and the thread taper is preferably 0.0625 inch per inch.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a front view of a swaging apparatus constructed in accordance with this invention.

[0011]FIG. 2 is a sectional view of one of the rollers of the apparatus of FIG. 1, taken along the line 2-2 of FIG. 1.

[0012]FIG. 3 is a sectional view of the swaging apparatus of FIG. 1, taken the along the line 3-3 of FIG. 1 and shown with only one of the rollers.

[0013]FIG. 4 is a sectional view of a pipe after swaging and prior to being threaded.

[0014]FIG. 5 is a sectional view of the pipe of FIG. 4 after being threaded and coupled to a collar.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Referring to FIG. 1, swaging apparatus 11 has a head 13, which is a large circular plate of steel. It may have a hole 15 in its center, hole 15 being concentric with an axis of rotation 17. A plurality of holes 19 (FIG. 3) are spaced in a circular array around hole 15. Holes 19 are parallel and concentric with axis 17.

[0016] As shown in FIG. 2, a shaft 21 extends into each of the holes 19. A roller 23 is rotatably mounted to a supporting portion of shaft 21 located on the forward side of head 13. Each roller 23 has a conical tapered exterior 25 that has a taper is in the range from 0.035 to 0.0625 inch per inch. A set of bearings 27 supports each roller 23 on each shaft 21.

[0017] While holes 19 could be threaded for receiving shafts 21, preferably each shaft 21 extends completely through one of the holes 19 as shown in FIG. 2. Each shaft 21 has a threaded end 29 on the rearward side of head 13 that receives a nut 31.

[0018] A chucking plate 33 is mounted to the rearward side of head 13. In the preferred embodiment, chucking plate 33 is a circular steel plate having approximately the same outer diameter as head 13. Chucking plate 33 has a perimeter wall 35 on its forward side that engages an annular recess 37 formed on the rearward side of head 13. Once abutted, as shown in FIG. 3, a cavity 39 will be defined between the rearward side of head 13 and a forward side of chucking plate 33. The threaded ends 29 and nuts 31 of each shaft 21 locate within cavity 39. Chucking plate 33 may optionally have a central hole 41 that is coaxial with axis 17 (FIG. 1).

[0019] A plurality of mounting holes 43 are spaced around the perimeter of chucking plate 33. Mounting holes 43 align with mounting holes 45 in head 13. Fasteners (not shown) are employed to extend through holes 43 and 45 and secure chucking plate 33 to head 13. A circular hub 47 is formed on the rearward side of chucking plate 33. Hub 47 is of a considerably smaller diameter than perimeter wall 35 and protrudes rearwardly a short distance from the rearward side of chucking plate 33. Hub 47 is concentric with hole 41 and axis 17 (FIG. 1). A rotary machine such as a large lathe will clamp about hub 47 to rotate chucking plate 33 and head 13. Although shown with a separate chucking plate 33, head 13 could be formed so that it is engaged by a rotary member directly.

[0020] Referring to FIG. 4, a section of pipe 49 is shown after it has been swaged with swaging apparatus 11. Pipe 49 is of steel for forming thin wall casing. Typically it will be manufactured by rolling a flat plate into a cylinder, then welding the seam. However, pipe 49 could be formed in other manners. Pipe 49 has an outer diameter 51 preferably in the range from 4½″ to 5½″. Its wall thickness between its outer diameter 51 and inner diameter 53 is in the range from 0.125″ to 0.219″, and preferably about 0.156″.

[0021] Swaged section 55 has been swaged by swaging apparatus 11, resulting in both a tapered exterior 57 and tapered interior 59, which are at approximately the same taper angle. In the preferred embodiment, tapered exterior 57 is in the range from 0.035 to 0.0625 inch per inch, and preferably 0.035 inch per inch. The engagement of rollers 23 on exterior 57 results simultaneously in the formation of tapered interior 59.

[0022] Threads 61 are then formed on swaged section 55. Threads 61 are preferably conventional API threads, such as eight threads per inch having a triangular shape. Threads 61 are also cut on a taper that is equal to or greater than the taper of swaged section 55. Preferably the crests of the threads 61 will have a taper that is 0.0625 inch per inch. In the preferred embodiment, which has a taper of 0.035 inch per inch on swaged section exterior 57, the remaining wall thickness through swaged section 55 will thus decrease from end 62 to rim 60 after threading. The depth of threads 61 is uniform at about 0.07125 inch throughout swaged section 55 except at the thread run out at end 62. The difference in the taper of threads 61 and the taper of swaged section exterior 57 is selected so as to avoid unduly reducing the wall thickness of the supporting metal under threads 61 near pipe rim 60. A conventional collar 63 having mating threads is shown secured to threads 61 in FIG. 5.

[0023] In operation, pipe 49 is held against rotation while swaging apparatus 11 rotates about axis 17. Swaging apparatus 11 and pipe 49 are then brought together, normally by advancing swaging apparatus 11 linearly toward pipe 49. Alternately, pipe 49 could be moved toward swaging apparatus 11, or both moved toward each other. Rollers 23 will begin to engage the cylindrical exterior of the end of pipe 49 as pipe 49 is continually advanced toward swaging head 13. Rollers 23 will form tapered exterior 57 on swaging section 55 as illustrated. After swaging, threads 61 are cut on swaging section 55 in a conventional manner beginning at pipe rim 60. The length of threaded section 61 is the same as the length of swaging section 55.

[0024] The invention has significant advantages. The swaged ends allow tapered threads to be cut on thin wall pipe without unduly reducing the supporting metal wall thickness near the pipe rim. This pipe is able to meet tensile tests. The swaging machine is fast and efficient. The rollers can be readily removed for replacement.

[0025] While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. 

I claim:
 1. An apparatus for swaging pipe, comprising: a head having an axis of rotation and a plurality of holes spaced in a circular array concentric and parallel with the axis of rotation; a plurality of shafts, each located in one of the holes, each of the shafts having a supporting portion located on a forward side of the head; a plurality of rollers, each rotatably mounted to the supporting portion of one of the shafts, each of the rollers having a conical exterior for rotatably engaging and swaging an end of a pipe as the head rotates; and a chucking member on a rearward side of the head for engagement by a rotary member to rotate the head.
 2. The apparatus according to claim 1 wherein the chucking member comprises: a plate having a forward side and a rearward side; a hub on the rearward side of the plate concentric with the axis of rotation of the head for engagement by the rotary member; a circular wall protruding from the forward side of the plate, the wall engaging the rearward side of the head, defining a central cavity between the rearward side of the head and the forward side of the plate; and wherein the shafts extend through the holes and have rearward ends that protrude into the cavity.
 3. The apparatus according to claim 1 further comprising a set of bearings located between each supporting portion of each of the shafts and each of the rollers.
 4. A method of manufacturing oil well casing, comprising: (a) providing a swaging head with an axis, a plurality of holes in a circular array concentric and parallel with the axis, a shaft located in each hole, and a tapered roller rotatably mounted on each of the shafts; (b) rotating the swaging head and bringing the tapered rollers into contact with an end of a cylindrical steel pipe, which is held against rotation, to provide a conical section with an exterior having a selected taper; then (c) cutting a set of threads on the exterior of the conical section.
 5. The method according to claim 4, wherein the pipe has a wall thickness in the range from 0.125 inch to 0.219 inch.
 6. The method according to claim 4, wherein the pipe has an outer diameter in the range from 4½ inches to 5½ inches.
 7. The method according to claim 4, wherein the pipe has a wall thickness in the range from 0.125 inch to 0.219 inch, and the pipe has an outer diameter in the range from 4½ inch to 5½ inch.
 8. The method according to claim 4, wherein in step (c), the threads are cut on a taper angle that is equal to or greater than the taper formed in step (b).
 9. The method according to claim 4, wherein in step (c), the threads are cut on a taper angle that is greater than the taper formed in step (b).
 10. The method according to claim 4, wherein the taper formed in step (b) is in the range from 0.035 inch per inch to 0.0625 inch per inch, and the threads are formed in step (c) on a taper that is 0.0625 inch per inch.
 11. A method of manufacturing oil well casing, comprising: (a) providing a cylindrical steel pipe with an outer diameter in the range from 4½ inch to 5½ inch and a wall thickness in the range from 0.125 inch to 0.219 inch; (b) swaging a first end of the pipe to provide a conical section with an exterior having a taper in the range from 0.035 inch per inch to 0.0625 inch per inch; then (c) forming a set of threads on the exterior of the conical section having a taper that is not less than the taper formed in step (b).
 12. The method according to claim 11, wherein: step (b) further comprises swaging a second end of the pipe to provide a conical section with an exterior having a taper in the range from 0.035 inch per inch to 0.0625 inch per inch; and step (c) further comprises forming a set of threads on the exterior of the conical section of the second end of the pipe with a taper that is not less than the taper on the conical section of the second end of the pipe.
 13. The method according to claim 11, wherein: the taper of the threads in step (b) comprises 0.0625 inch per inch.
 14. The method according to claim 11, wherein: step (b) comprises providing a swaging head with an axis, a plurality of shafts mounted to the swaging head in a circular array concentric and parallel to the axis of the swaging head, and a plurality of tapered rollers, each mounted to one of the shafts; then rotating the swaging head while preventing rotation of the pipe and bringing the tapered rollers and the first end of the pipe into contact with each other.
 15. A well casing, comprising: a pipe having an outer diameter in the range from 4½ inch to 5½ inch and a wall thickness in the range from 0.125 inch to 0.219 inch; a swaged section on each end of the pipe, the swaged section having an exterior with a taper; and a set of threads formed on the exterior of each of the swaged sections, the threads having a taper that is at least equal to the taper formed on the exterior of the swaged section.
 16. The well casing according to claim 15 wherein the taper on the exterior is in the range from to 0.035 inch per inch to 0.0625 inch per inch, and the taper of the threads is 0.0625 inch per inch. 